minissdpd(1) listen to SSDP traffic on the network so miniupnpc(3) does
not need to perform the discovery process and can work faster to set up
a redirection. minissdpd(1) is also able to reply to M-SEARCH SSDP
requests on behalf on miniupnpd(1) or other UPnP server software. That
is useful in order to host several UPnP services on the same machine.
miniupnpd(1) natively uses minissdpd(1) if run on the same machine, but
other UPnP software may require to be patched.
